Water diversions are utilized to divert water from rivers and streams to generate hydropower. Water diversions are also utilized to divert water for agricultural, industrial and municipal water uses. One component of a typical water diversion is a low-head dam or weir. The dam creates a pool where water can be reliably withdrawn through an intake. While these dams can be effective for their intended purposes, they are well known for creating hazards for fish and recreational river users, such as “boaters” and “river runners”.
FIG. 1 illustrates a conventional screened water diversion system 10 for diverting water on a river 12. The screened water diversion system 10 includes a low head dam 14 which forms a relatively large upstream pool 16 and a downstream pool 18 in the river 12. The screened water diversion system 10 also includes a hydraulic gate 20 which channels water to a turbine (not shown) or other water-using system, and a trash rack 26 which prevents debris from entering the diverted flow.
One potential hazard for recreational rivers users produced by the low head dam 14 is illustrated in FIG. 2. In particular, the water flow 22 over the low head dam 14 forms a reversed water flow 24 in the downstream pool 12, which can trap recreational rivers users and their watercraft. The hydraulic gate 20, the trash rack 26 and various appurtenances of the screened water diversion system 10 also produce potential hazards for recreational rivers users. These prior art structures also create conditions which: 1.) negatively impact fish habitat and passage; 2.) are expensive to build and maintain; 3.) raise the upstream water surface elevation (due to the low head dam 14), which can adversely affect the floodplain and worsen flooding; 4.) impact the ability of the river to transport sediments; and 5.) require removal of sediments from the upstream pool.
Referring to FIG. 3, another hazardous screened water diversion system is illustrated. In particular, the screened water diversion system can also include a screen assembly 28 associated with the hydraulic gate 20. The screen assembly 28 removes filtered diverted water flow 30 from debris laden flow in the river or channel. A bypass water flow 32 carries the debris, and fish as well, back into the water flow 22 on the river 12. As shown in FIG. 3A, the screen assembly 28 includes a tilted wedge wire screen 29 having backing bars 40, and wedge wire elements 34 attached to the backing bars 40. The tilted wedge wire screen 29 is also known in the art as a COANDA screen. U.S. Pat. No. 4,415,462 to Finch et al.
As shown in FIG. 3, the screen assembly 29 is oriented such that the tilted wedge wire screen 29 (FIG. 3A) has a steep back slope in the flow of water 22. As shown in FIG. 3A, the wedge wire elements 34 are spaced to form openings 36 for water flow 38 through the tilted wedge wire screen 29, which travels along the profile of the wedge wire elements 34. As also shown in FIG. 3A, the wedge wire elements 34 are oriented at an angle “a” relative to the water flow 22, which produces a shearing action which forces a diverted flow 30 (FIG. 3) through the tilted wedge wire screen 29. The tilted wedge wire screen 28 (FIG. 3) relies on a high “sweeping” velocity of the flow of water 22 across the tilted wedge wire screen 28 to keep the openings 36 (FIG. 3A) free of debris.
In addition to being hazardous to recreational river users and to fish, the tilted wedge wire screen 29 (FIG. 3A) requires a large amount of drop “hd” (FIG. 3) and creates the negative conditions outlined above. The large amount of drop “hd” also inhibits upstream fish passage and requires additional fish passage structures if upstream fish passage is required. Furthermore the tilted wedge wire screen 29 (FIG. 3A) is prone to drying up, which has a further negative impact on fish. The tilted wedge wire screen 29 (FIG. 3A) is negatively affected by high tailwater, which slows down the sweeping velocity of the water flow 22, allowing debris to accumulate in the openings 36 (FIG. 3A). A high tailwater in the downstream pool 18 (FIG. 3) can also cause a hydraulic jump to occur on the tilted wedge wire screen 29 (FIG. 3A) further plugging the tilted wedge wire screen 29 and decreasing diversion capacity. Still further, the tilted wedge wire screen 29 is usually placed close to or exposed to cold air such that frazzle ice can form and plug the openings 36 (FIG. 3A).
A variety of other water diversion systems have been constructed which include flat screens of various types with slow-velocity bypass water flow over the screens (sweeping velocities) so that the screens tend to plug or cannot be utilized if debris is present. Other water diversion systems screens are located so that they are not heavily influenced by debris or the water surface elevation in the downstream pool. These could include water diversion systems that have screens elevated far enough above the invert of a river or channel or in a river or channel which has a narrower range of water flows, or in a case where the minimum rate or water flow in the river or channel is much greater than the maximum rate of divert water flow.
In view of the shortcomings of conventional prior art water diversion systems, there is a need in the art for improved systems with components which are less hazardous to recreational river users and fish, which reduce impacts to the floodplain and the natural river morphology, and which pass sediment and debris. In addition, there is a need in the art for water diversion systems that are inexpensive to build and maintain, and which function efficiently over a wide range of environmental conditions.
However, the foregoing examples of the related art and limitations related therewith, are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.